Image sensors are used extensively in fax machines, still or video cameras, sensors, scanners, telescopes and the like. The image sensor field is dominated by two technologies, namely CCD (Charge Coupled Device) and CMOS (Complementary Metal oxide Semiconductor). Generally, image sensors are equivalently related to as image array sensors, focal plane sensors, and array photosensor. Image sensors convert radiant energy, often but not necessarily, in the visible and IR range, to electrical energy or signal.
Radiant energy extends over a very broad radiation spectrum, and the spectrum to which different aspects of the invention may be applicable ranges from the Ultra Violet (UV), through the visible light portion of the spectrum, to Infra Red (IR) and beyond into the millimeter wave range, also known as Extremely High Frequency (EHF) and in some applications even to the Super High Frequency (SHF) and microwave range. Many applications would need to cover only portions of this spectrum. It is seen therefore that the application at hand determines the spectral range of interest, and that a spectral range of interest may differ by application, an apparatus, or a portion thereof. Regarding lateral waveguides, yet another aspect described below, each waveguide may have its own spectrum of interest, which may differ from the spectral range of interest of an adjacent waveguide. Therefore, the spectral range of interest is defined herein as relating to any portion or portions of the total available spectrum of frequencies which is being utilized by the application, apparatus, and/or portion thereof, at hand, and which is desired to be detected and/or emitted utilizing the technologies, apparatuses, and/or methods of the invention(s) described herein, or their equivalents.
Structure to facilitate conversion of radiant energy to electricity or electrical signals (hereinafter “LE”), or conversion of electrical signals into radiant energy such as light (hereinafter “EL”) are known. Collectively, objects, materials, and structures, which perform conversion between two forms of energy, or adjust and control flow of energy, are known by various names which denote equivalent structures, such as converters, transducers, absorbers, detectors, sensors, and the like. To increase clarity, such structures will be referred to hereinunder as ‘transducers’. By way of non-limiting examples, the term “transducer” relates to light sources, light emitters, light modulators, light reflectors, laser sources, light sensors, photovoltaic materials including organic and inorganic transducers, quantum dots, CCD and CMOS structures, LEDs, OLEDs, LCDs, receiving and/or transmitting antennas and/or rectennas, phototransistors photodiodes, diodes, electroluminescent devices, fluorescent devices, gas discharge devices, electrochemical transducers, and the like.
A transducer of special construction is the RL transducer, which is a reflective transducer. Reflective transducers controllably reflect radiant energy. Such transducers may comprise micromirrors, light gates, LCD, and the like, positioned to selectively block the passage of radiant energy, and reflect it into a predetermined path, which is often but not always, the general direction the energy arrived from. Certain arrangements of semiconductor and magnetic arrangements may act as RL transducers by virtue of imparting changes in propagation direction of the radiant energy, and thus magnetic forces or electrical fields may bend a radiant frequency beam to the point that in effect, it may be considered as reflected. RL transducers may be fixed, or may be used to modulate the energy direction over time. Passive transducers such as LCD and micromirrors fall into the reflective device when used to reflect incoming energy, but when used in conjunction with at least one light source may be considered LE type transducers.
Presently the most common structures for LE conversion are photovoltaic (PV) which generally use layers of material forming a P-N junction. Charge Coupled Devices (CCD), and Complementary Metal Oxide Semiconductor (CMOS) are two common type of image sensing technology for the visual range, while HgCdTe (Mercury Cadmium Telluride) is commonly used in infrared sensing applications.
Other types of transducers utilize antennas, and more commonly rectennas, to achieve the energy conversion. The term rectenna relates to an antenna structure having a rectifier integrated with, or closely coupled to, the antenna, such that electromagnetic energy incident on the antenna is rectified and presented as primarily unidirectional (ideally DC) signal. By way of example, rectennas are described in U.S. Pat. No. 7,799,998 to Cutler, and in “Nanoscale Devices for Rectification of High Frequency Radiation from the Infrared through the Visible: A New Approach”, N. M. Miskovsky, P. H. Cutler, A. Mayer, B. L. Weiss, BrianWillis, T. E. Sullivan, and P. B. Lerner, Journal of Nanotechnology, Volume 2012, Article ID 512379, doi:10.1155/2012/512379, Hindawi Publishing Corporation©. which is incorporated herein by reference in its entirety.
Waveguides are a known structure for trapping and guiding electromagnetic energy along a predetermined path. An efficient waveguide may be formed by locating a layer of dielectric or semiconducting material between cladding layers on opposite sides thereof, or surrounding it. The cladding may comprise dielectric material or conductors, commonly metal. Waveguides have a cutoff frequency, which is dictated by the wave propagation velocity in the waveguide materials, and the waveguide width. As the frequency of the energy propagating in the waveguide approaches the cutoff frequency Fc, the energy propagation speed along the waveguide is slowed down. The energy propagation of a wave along a waveguide may be considered as having an angle relative to cladding. This angle is determined by the relationship between the wavelength of the wave and the waveguide width in the dimension in which the wave is being guided. If the width of the waveguide equals one half of the wave wavelength, the wave reaches resonance, and the energy propagation along the waveguide propagation axis stops. The condition where energy is at or close to such resonance will be termed as a stationary resonant condition.
Tapered waveguide directed at trapping radiant energy, as opposed to emitting energy via the cladding, have been disclosed by Min Seok Jang and Harry Atwater in “Plasmionic Rainbow Trapping Structures for Light localization and Spectrum Splitting” (Physical Review Letters, RPL 107, 207401 (2011), 11 Nov. 2011, American Physical Society©). The article “Visible-band dispersion by a tapered air-core Bragg waveguide”, (B. Drobot, A. Melnyk, M. Zhang, T. W. Allen, and R. G. DeCorby, 8 Oct. 2012/Vol. 20, No. 21/OPTICS EXPRESS 23906, ©2012 Optical Society of America “Visible-band dispersion by a tapered air-core Bragg waveguide” B. Drobot, A. Melnyk, M. Zhang, T. W. Allen, and R. G. DeCorby, 8 Oct. 2012/Vol. 20, No. 21/OPTICS EXPRESS 23906, ©2012 Optical Society of America) describes out-coupling of visible band light from a tapered hollow waveguide with TiO2/SiO2 Bragg mirrors. The mirrors exhibit an omnidirectional band for TE-polarized modes in the ˜490 to 570 nm wavelength range, resulting in near-vertical radiation at mode cutoff positions. Since cutoff is wavelength-dependent, white light is spatially dispersed by the taper. These tapers can potentially form the basis for compact micro-spectrometers in lab-on-a-chip and optofluidic micro-systems. Notably, Bragg mirrors are very frequency selective, complex to manufacture, and require at least a width higher than ¾ wavelength to provide any breadth of spectrum. In addition to the very narrow band, the Bragg mirrors dictate a narrow bandwidth with specific polarization, while providing however a fine spectral resolution.
A Continuous Resonant Trap Refractor (CRTR) is the name used in these specifications to denote a novel structure which is utilized in many aspects of the present invention. As such, a simple explanation of the principles behind its operation is appropriate at this early stage in these specifications, while further features are disclosed below.
A CRTR is a structure based on a waveguide having a tapered core, the core having a wide base face forming an aperture, and a narrower tip. The core is surrounded at least partially by a cladding which is transmissive of radiant energy under certain conditions. The CRTR may be operated in splitter mode, in a mixer/combiner mode, or in a hybrid mode providing combination of mixer and splitter mode. In splitter mode the radiant energy wave is admitted into the CRTR via the aperture, and travels along the depth direction extending between the aperture and the tip. The depth increases from the aperture towards the tip, such that larger depth implies greater distance from the aperture. The core is dimensioned such that at least some of the admitted frequencies will reach a state where they will penetrate the cladding, and be emitted therefrom. This state is referred to as Cladding Penetration State (CPS), and is reached when energy of a certain frequency approaches a critical width of the waveguide for that frequency. The mechanism at which cladding penetration state occurs may vary, such as by tunneling penetration, skin depth penetration, a critical angle of incidence with the cladding and the like. Generally CPS will occur in proximity to, or at the width, where the wave reaches a resonance, known as the critical frequency for that width, and conversely as the critical width for the frequency, of the wave. Regardless of the mechanism, a CPS is characterized by the wave reaching a frequency dependent depth within the CRTR where it is emitted via the cladding. The decreasing width of the core will dictate that a lower frequency wave will reach CPS before higher frequency waves, and will penetrate the cladding and exit the waveguide at a shallower depth than at least one higher frequency wave. As waves of differing frequencies will be emitted via the cladding at differing depths, the CRTR will provide spatially separated spectrum along its cladding. Notably, in certain CRTR embodiments some frequency components of the incoming energy may be emitted via the tip, in non-sorted fashion.
Conversely, when operated in mixer/combiner mode, a wave coupled to the core via the cladding, at, or slightly above, a depth where it would have reached CPS in splitter mode, will travel from the emission depth towards the aperture, and different waves coupled to the core through the cladding will be mixed and emitted through the aperture. Coupling light into the CRTR core from the cladding, will be referred to as ‘injecting’ or ‘inserting’ energy into the CRTR. It is noted that in most if not all practical cladding materials the light will refract when entering and exiting the cladding. Therefore, the light source will be located at a different depth than the point of desired entry into the core. The depth at which the wave would couple into the tapered core is somewhat imprecise, as at the exact depth of CPS the wave may not couple best into the core, thus the term ‘slightly above’ as referred to the coupling of light into the tapered core in combiner/mixer mode should be construed as the depth at which energy injected into tapered core via the cladding would best couple thereto to be emitted via the aperture, within certain tolerances stemming from manufacture considerations, precision, engineering choices and the like.
The term spectral component will relate to energy portion of the energy at the aperture, which is characterized by its frequency, polarization, phase, flux, intensity, incidence, radiosity, energy density, radiance, or a combination thereof.
The term tapered should be construed as extending beyond a simple linear taper, and should extends to stepped tapers, tapers that follow any desired profile, and even to tapers which are uneven about a width plane. Thus while the width o a tapered core may monotonically decrease, the taper relates to the core as a whole, and does necessitate monotonic width reduction in each direction and/or with each successive width plane.
A round cross section of the tapered core will be polarization neutral under most circumstances. Certain non-symmetrical or multi-faceted symmetrical tapered core forms will however cause separation of the aperture-admitted radiant energy to be polarization sensitive. Thus, by way of example, a square pyramid or frustum CRTR core will separate incoming radiant energy into its component polarizations as well as by its frequency. Thus if two transducers are disposed in a first and a second path of energy emitted via the cladding, the first path exits the core at a first face, and second path exists the core at a second face disposed at an angle to the first face, the first transducer will receive a spectral component which differs from the spectral component received by the second face, at least by different polarization. This behavior will be reversed when the CRTR operates in mixer/combiner mode, such that energy emitted from the aperture will reflect the polarity created by separate sources, and injected into the CRTR at different faces. By way of none-limiting example, if light source A injects modulated energy into one face of the pyramidal core, and light source B injects differently modulated energy into a perpendicular face of core, the light emitted by the aperture will have one spectral component at a first polarization reflecting the modulation of source A, and a second spectral component at 90° to the first spectral component, representing the modulation of source B. Therefore, Placing a plurality of EL transducers at different angular locations about the depth dimension of the CRTR, would result in combined polarized energy corresponding to the location of the transducers, being emitted via the aperture, when the transducers are energized.
CRTRs may also operate in reflective mode, by providing light gates which will reflect radiant energy back into the CRTR tapered core. A light gate disposed at the depth where radiant energy is emitted out of the cladding, will cause the emitted energy to be reflected back into the cladding, and thence emitted via the aperture. An array of CRTRs in conjunction with RL transducers which act as light-gates will have variable reflectivity such that at least a portion of the light incident on the array at the associated frequency will be reflected, in accordance with the setting of the light gate reflectors. The term light gate should be construed to extend to the complete spectral range of interest, which is dictated by the application at hand. Therefore, a light gate may reflect energy well beyond the visible light. The broad band capabilities of the CRTR allows modulation of its reflectance over a broad band of frequencies, extending the ability for reflectance into the UV, IR, and even the mm wave spectrum. Reflective mode may also operate in polarization sensitive mode as explained above for EL and LE transducers in polarization sensitive mode.
A CRTR is considered to operate in hybrid mode when energy is both admitted and emitted via the aperture. In certain embodiment this mode involves energy being admitted via the aperture and at least portions thereof being emitted via the cladding, while other energy is being injected via the cladding and emitted via the aperture. In other embodiments a portion of the energy admitted via the aperture is selectively reflected back therethrough. A reflective CRTR is a CRTR cooperating with at least one RL transducer, and is also considered to operate at hybrid mode.
Thus functionally, a CRTR is a device which allows passage of radiant energy therethrough, while                a. imparting a change in the direction of propagation of incoming energy;        b. in one mode a CRTR is operational to spatially disperses incoming energy into spatially separated spectral components thereof, which are outputted via the CRTR cladding, the mode is equivalently referred to as disperser, splitter, or dispersion mode;        c. in another mode a CRTR is operational to combine a plurality of incoming spectral components into emitted energy comprising the components and emitted via the aperture, the mode equivalently referred to as combiner, mixer, or mixing mode; and,        d. in another mode the CRTR is operational to controllably reflect at least a portion of the spectral components admitted via the aperture, the reflected components being reflected via the aperture, thus controllable changing the effective reflectance of the CRTR at selected spectral components, the mode equivalently referred to as reflective mode or reflectance mode.        As presented elsewhere in these specifications, a CRTR may be operated in a combination of these modes, and such mode is considered a hybrid mode.        
A simplified view of a CRTR is provided in FIG. 1A. A CRTR comprises a waveguide having a tapered core 73 and a cladding 710; the core having an aperture and a tip. The larger face (denoted Hmax) of the tapered waveguide core will be generally referred to as the CRTR aperture, and the smaller face, which may taper to a point, will generally be referred to as the tip. The axis X-X extending between the aperture and the tip would be referred to as the CRTR depth axis. The width of a two dimensional CRTR is transverse to the depth direction which may be considered a width plane, while for a three dimensional CRTR, at any depth the CRTR has a plurality of widths transverse to the depth direction. The different widths for a single depth form a width plane, which is transverse to the depth direction, and the term in at least one direction′ as related to width, relates to directions on the width plane or parallel thereto. Any given depth correspond with its width plane, and thus there are infinite number of parallel width planes.
Radiant energy 730 admitted via the aperture travels generally along the depth axis; however, the energy may travel towards the aperture in mixer mode, away therefrom in splitter mode, or in both direction in any hybrid and/or reflective modes. In splitter mode a CRTR acts as a spectral splitter by admitting energy within a spectral range of interest via the aperture and emitting it in a frequency sorted fashion via the cladding. A CRTR operating in mixer mode admits radiant energy via the cladding and mixes and emits the energy via the aperture. Notably, a certain angle shift occurs in the process, and thus, energy entering the CRTR from its aperture will be angled away, i.e. refracted, and emitted at an angle to the depth dimension in a splitter mode. In mixer mode energy entering the CRTR via the cladding will couple to the core and would be angled away from the direction in which it was injected, to propagate generally along the depth axis and emitted via the aperture. The core width varies in magnitude so as to be greater at the first end than at the second end. The core width is also dimensioned such that when multi-frequency energy is admitted through the core and propagates along the core depth, it will cause a lower frequency spectral component to reach a cladding penetration state at a first depth, and the core will further taper to a width that will cause energy of a higher frequency spectral component reach a cladding penetration state at a second depth, which is larger than the first depth. In many embodiments, this is achieved by having the width dimension taper to a size smaller than half wavelength of the shortest wave in the spectral range of interest of the CRTR, but in certain embodiments a portion of the spectral range of interest is emitted via the tip.
At its wider base known as the aperture, the CRTR has a width Hmax, which limits the lowest cutoff frequency Fmin. At the tip the tapered core width Hmin dictate a higher cutoff frequency Fmax. Between the aperture wide inlet and the narrower tip, the cutoff frequency is continually increased due to the reduced width. Energy, such as polychromatic light 730 is incident the aperture at an angle which permits energy admission. Waves having a lower frequency than the cutoff frequency Fmin are reflected 735. Waves 740 having frequency higher than Fmax exit through the CRTR core, if an exit exists. Waves having frequencies between Fmin and Fmax will reach their emission width, and thus their cladding penetration state, at some distance from the inlet of the waveguide depending on their frequency. The distance between the inlet and the emission width of a given frequency is the emission depth.
Thus, examining the behavior of a wave of arbitrary frequency Ft, where Fmin<Ft<Fmax, which enters into the CRTR core at its aperture at an incidence angle within an acceptance cone centered about the propagation axis X-X, the angle θ between the wave and X-X will vary as the wave propagates along the X-X axis due to the narrowing of the CRTR waveguide and increase of the cutoff frequency, as depicted schematically by Ft′. As the wave approaches depth X(Ft) where either the tapered waveguide cutoff frequency equals or nearly equals Ft, or the angle θ approaches the critical angle θc, at which the wave can not propagate any further within the CRTR core. The wave Ft is thus either radiated through the dielectric cladding of the CRTR as shown symbolically by 750 and 752, or is trapped in resonance at depth X(Ft) in a metal clad CRTR. At that point the wave of frequency Ft reached its cladding penetration state at the emission depth dictated by the emission width of the tapered CRTR core. For a continuum of entering waves of different frequencies Fmin<F1, F2, . . . Fx<Fmax, entering the base of the tapered core waveguide 71, it becomes a Continuous Resonant Trap Refractor (CRTR) in which the different frequency waves become standing waves, trapped at resonance in accordance to their frequency along the X-X axis. Such trapped waves are either leaked through the cladding by the finite probability of tunneling though the cladding or are lost to absorption in the waveguide. Note that since a CRTR will in general also cause admitted rays (speaking from the perspective of a CRTR operating in splitter mode) to be refracted or otherwise redirected so that the component(s) produced by splitting exit the CRTR at an angle to the CRTR depth axis, this will make it possible to employ a CRTR that has been embedded within stacked waveguides in such a manner that the CRTR directs specific components, e.g., spectral components, of the incoming multispectral radiation to predetermined waveguides.
Therefore, for a given CRTR spectral range of interest Si, ranging between λmax to λmin which represent respectively the longest and shortest wavelengths of the spectral range of interest as measured in the core material, wherein λ′ is at least one wavelength in Si, the dimensions of a frequency splitting CRTR taper are bounded such that    a. the aperture size ψ must exceed the size of one half of λmax;    b. the CRTR core size must also be reduced at least in one dimension, to at least a size ζ which is smaller than or equal to one half of wavelength λ′.
Thus the CRTR dimensions must meet at least the boundary of {ζ≦λ′/2<λmax/2≦ψ} where the CRTR sizes defined above relate to a size in at least one dimension in a plane normal to the depth dimension. In FIG. 4 the aperture size ψ=hmax. It is noted however that not all waves in Si must meet the condition b. above. By way of example, certain waves having shorter wavelengths than hmin/2 may fall outside the operating range of the CRTR. Such waves which enter the CRTR will either be emitted through the tip, reflected back through the aperture, or absorbed by some lose mechanism.
Notably if a third spectral component λ″ is present, and has a higher frequency than λ′, it may be emitted at greater depth than λ′ or be emitted or reflected via the tip, if the tip is constructed to pass a spectral component of frequency λ″.
It was already noted that CRTR use may extend to the millimeter wave range (EHF), or even to the microwave range. Between cm waves and micron IR radiant energy the range of available dielectric constants increases dramatically. By way of example, water has an index of refraction of nearly 10 at radio frequencies but only 1.5 at IR to UV. There are numerous optical materials with low and high index at mm wave frequencies and below. Thus while the principles of operation of CRTRs are similar, the materials and sizes differ.
A millimeter/microwave operated CRTR is a channelized filter integrated into a horn antenna wherein the channelized ports are lateral to the horn and the in-line exit port is a high pass filtered output for a broad band input. Such device may be utilized as an excellent front end for a multiplexer/duplexer, and as a general purpose antenna that has excellent noise figure and improved anti-jamming as those characteristics are determined at the front end of devices which use them.
CRTRs are often disposed within a stratum. In some embodiments stratums comprise a plurality of superposed waveguides equivalently referred to as superposed waveguides, stacked waveguides, or lateral waveguides. Another type of stratum comprises a slab of material that is transmissive of the radiant energy spectral range of interest. The CRTRs are disposed such that the CRTR depth direction is substantially perpendicular to the local plane of the stratum. Radiant energy emitted from the cladding is coupled to transducers within the stratum or via the stratum, and radiant energy from EL transducers within the stratum is coupled to the CRTR via the cladding. A CRTR is considered “embedded’ or ‘disposed’ within a stratum where at least a portion of it is coupled to the stratum, and complete envelopment is not required.
In many embodiments that utilize lateral waveguide based stratum, transducers are embedded within the lateral waveguide. In certain embodiments the transducers are optimized for the frequency which is in the spectral range to which the corresponding waveguide is exposed. Conversely in certain embodiments the dimensions of the lateral waveguide is optimized for a transducer which emits energy of a certain frequency, however those are not requirements to many of the aspects of the present invention.
When combined with transducers, CRTRs are capable of providing a hyperspectral or multi-spectral pixels, which may be arranged in arrays. Those pixels act as a reversible channelized filter of light and other radiant energy, capable of operating from the long IR—and even to the millimeter wave radar and microwave regimes of the electromagnetic spectrum—to the deep UV. CRTRs are further capable of energy harvesting, as the channelized outputs are converted to electrical energy using photovoltaic and related processes.
CRTR based sensing pixels (generally referred to hereinafter as sensing pixels) utilize the CRTR or a portion thereof in splitter mode, to admit a broad bandwidth of energy via the aperture, and selectively channel portions of the admitted spectrum into frequency and/or polarization dependent locations, where the incoming energy may be converted into electrical energy by a plurality of LE transducers, the ordered outputs of which correspond to an image portion sensed by the pixel. Thus the sensing pixel is a combination of a CRTR and at least one EL transducer. Optionally a sensing pixel may also harvest some or all of the incoming energy for powering related circuitry, and/or emit energy.
CRTR based emitting pixels (generally referred to herein as emitting pixels) utilize the CRTR or portion thereof in mixer/combiner mode, to receive energy of varying spectral components via the cladding. The CRTR or a portion thereof is operated in mixer/combiner mode, where an array of weighted radiant energy sources serve as channelized inputs. Spectral components from the energy sources are fed into the CRTR core via the cladding, and are combined to emit the combined energy via the aperture, the spectral details of which are determined by the weighting of the spectral components of the energy sources. Different spectral components injected into the cladding will mix. Thus, by way of example, light of frequency Fr, injected through the cladding into the tapered waveguide core, will mix with the light of Fp. Therefore, assuming that the core material is equally transparent to components of the CRTR spectral range of interest, and that the optical loses in the core are negligible, the radiant energy emitted from the CRTR aperture would be the summation of the radiant energy injected into the core. The skilled in the art would readily recognize that by placing primary color light sources about the cladding any color light may be emitted through the aperture.
The term “about the cladding” or equivalently about the CRTR or its core, should be construed to mean being coupled to via energy path, which implies that the transducer is disposed about the cladding not only by being physically adjacent to the cladding, but also when an energy path such as beam propagation, waveguide, and the like, exists between the location where energy is transferred in or out of the cladding, and the transducer. Similarly, the disposition about the cladding is set by the location at which the energy exists or enters the cladding. Thus, by way of example if the transducer is coupled to the cladding via a waveguide such that the energy couples at depth A of the CRTR, the transducer is considered to be disposed at depth A regardless of its physical location relative to the RCTR.
A common application of emitting pixels is a display within the visual range, but the spectral content of the radiation emitted by the pixel may range beyond the visual range, ranging from mm wave to UV. Static images may be provided through constant weighting of energy sources in the primary colors range, while photographic, video, and patterns may be provided by actively varying the weights of energy sources in an array of pixels. Thus the emitting pixel is a combination of a CRTR and at least one EL transducer. Optionally an emitting pixel may also harvest some incoming energy for powering related circuitry, and/or sense energy in certain bands. A common application of splitter pixels is image array sensors, solar energy harvesting, and the like.
Pixels may also have variable weighted reflectors located on one or more channelized ports such that at least a portion of the light incident on the CRTR based pixel aperture, at the associated channel frequencies is programmably reflected. The reflectors form the RL type transducers disclosed above.
The path which a spectral component takes between the CRTR and its respective transducer constitute the channel. Channels may take many forms, such as lateral waveguides, paths within a slab stratum, other waveguides, and the like. A channel may also constitute a path between the CRTR core and a RL transducer even if such path is of minute length. In certain application the channel may be to an absorber which absorb the energy for storage, dispensing, as heat, and the like.
Frequency translation of one frequency of radiant energy to another are commonly utilized, such as translation of Infra Red (IR) light into the visible spectrum. Image amplification is also commonly used, by sensing light at certain portions of the spectrum and amplifying the sensed information by analog or digital means such as photon multiplication, on chip gain multiplication, and the like. Regardless of the technology through which an image is detected and redisplayed, there exists an ongoing demand for ever-improving signal to noise ratio, size weight and power (SWAP) reductions, pixel size reductions, and resolution improvements. There is a further need to efficiently combine detection methods in a single apparatus, such that an apparatus might augment low-light images with thermal imaging data and/or active IR illumination. Further needs of vision related devices may include dynamic change of light transmission in all or a portion of the spectrum, in response to certain environments and the changes therewithin.
In some cases, thermal sources might not be imaged with adequate resolution or certainty due to neighboring materials that are reflective to the IR frequencies being imaged. Such IR reflectors are often polarization dependent reflectors due to the Brewster angle associated with one polarization and the efficient reflection of the other. Active and thermal sources will typically emit randomly polarized light while reflected images will exhibit some polarization preferences. Thus, a method of polarization selective detection is also desirable.
Regardless of the technology through which an image is detected and redisplayed, there exists an ongoing demand for ever-improving signal to noise ratio, size weight and power (SWAP) reductions, pixel size reductions, and resolution improvements. There is a further need to efficiently combine detection methods in a single apparatus, such that an apparatus might augment low-light images with thermal imaging data and/or active IR illumination by way of example. In certain applications, incorporating energy harvesting methods is also desired.
For brevity and improved clarity the term ‘light’ as used herein is directed to being but one example of the frequency within the spectral range of interest, and inclusive thereof, unless specifically limited, such as ‘visible light’, infra red light, and the like. Thus the term light will be used as equivalent to radiant energy in the spectrum of interest.
Radiant energy of sufficiently high frequency may also be considered as a flow of photons, which are quantized units of energy which increases with frequency. Therefore certain terms that are common to simple electromagnetic energy need to be better specified as relating to the spectral range of interest. Thus, a dielectric material in the above mentioned energy spectrum may be defined as a material having low conductivity, and having a band-gap between a filled valence band and an empty conduction band exceeding the energy of any photon in the spectral range of interest to a specific application. A “semiconductor” refers to a photovoltaicly active material, having a bandgap comparable to or smaller than the photon energy of any photon in the spectral range of interest to a specific application. It is explicitly noted that a material that is a dielectric in one range of wavelengths may be an intrinsic semiconductor in a shorter wavelength region of the spectrum. Therefore the classification of a material as dielectric or semiconductor is determined by the structure and the frequencies at which it is intended to be used. Given the wide range of spectrum of interest in at least some applications the same material may be considered a dielectric in one location and a semiconductor in another.
In contrast, a transparent conductor is a material having a finite but meaningful conductivity due to a partially filled conduction band or partially empty valence band but having a band-gap between the valence band and conduction band exceeding the energy of any photon in the spectral range of interest. These materials act like a dielectric at some frequencies and like a semiconductor at even higher frequencies, but act like a conductor at low frequencies. Transparent dielectric materials also have low optical losses such that photons efficiently transmit through such material, at least at the spectral range of interest or a significant portion thereof for which they are employed.
While transparent conductors may be considered as wide bandgap semiconducting materials, they are used as conductors in most applications. Dielectrics, transparent conductors, and semiconductors, as used in these specifications, refer to materials that have a dielectric constant at optical frequencies; however the distinction between a semiconductor and the remaining materials is that the bandgap of a semiconductor is not substantially larger than the photon energy. As a general and non-limiting guideline, table 1 describes several characteristics of the different conductive, insulating, and semi-conductive materials.
TABLE IMaterialTransparentMetalConductorSemiconductorDielectricBandgap→ 0>>photon≦photon>>photonDChighgoodVaries→ 0ConductivityOpticalreflectivetransparentabsorptivetransparentPropertyDielectriccomplexlow losslossylow lossconstant
The term stationary resonance condition should be construed as relating to a situation in a waveguide where the frequency of the guided wave is sufficiently close to the local cutoff frequency of the waveguide, such that the guided wave reflects repeatedly between opposing surfaces of the guide. The corresponding energy velocity along the waveguide propagation axis is significantly lower than the speed of light in the bulk material of the waveguide and approaches zero at the stationary resonance condition. Notably, complete stationary resonant condition is an ideal limiting case which is almost never achieved.
The term Continuous Resonant Trap Refractor (CRTR) should be construed as relating to a tapered core waveguide having a base face and a tip. The larger face of the tapered waveguide core will be generally referred to as the aperture, and the smaller face, or point, will generally be referred to as the tip. Radiant energy travels along the depth direction extending between the aperture and the tip, however the radiant energy may travel towards the aperture, or away therefrom. For the purposes of these specifications, the depth increases from the aperture towards the tip, such that larger depth implies greater distance from the aperture. The term ‘tapered waveguide’ requires only that the waveguide core be tapered, and the overall dimensions or shape of the CRTR may be of any convenient shape.
A distance from the aperture along the depth dimension at which the width of the waveguide in at least one dimension would be the critical width which will block light of a given frequency from advancing further down towards the tip, is referred to in these specification as ‘emission depth’ for this frequency. The width of the CRTR core which causes the energy to be emitted through the cladding for a wave of a given frequency, is termed ‘emission width’ for that wave. Such emission occur at cladding penetration state. When radiant energy comprising a plurality of spectral components separated by frequency is admitted through the CRTR aperture, lower frequency waves will reach their emission depth before higher frequency waves. Thus, the CRTR will provide spatially separated spectrum along its cladding. In addition the CRTR refracts the spatially separated light away from the axis of the CRTR extending from the aperture toward the tip.
Cladding may comprise a dielectric material with lower refractive index than that of the core, a thin conductive layer with thickness comparable to the skin depth of the conductor, or a conductive layer with perforations. Such cladding and core systems offer total internal reflection for sufficiently thick claddings. As the wave is slowed the equivalent incident angle of the wave against the core/cladding boundary increases and penetration into the cladding increases up to the critical angle. For intermediate cladding thicknesses Frustrated Total Internal Reflection (FTIR) occurs just before the critical angle. For sufficiently thick claddings the wave is bound until the critical angle. Metallic claddings with small perforations or with thicknesses at or near the skin depth also have angle dependent reflection coefficients, resulting in a situation analogous to FTIR, and are thus also considered suitable.
Current technology, color sensors are generally obtained by either filtering colors into adjacent pixels, in a technique known as Bayer Filter, by using multi-layered pixels or by utilizing three separate sensors.
Bayer filters utilize pixel filters of different colors laid over adjacent pixels. In the Foveon 3X© system (Foveon© Inc., Santa Clara, Calif., USA), three different layers are stacked on top of each other, each layer being sensitive to one primary color. The stacked transducer layers of the same bandgap or of differing bandgap have been shown to improve efficiency and image quality over filter based image sensors. Detecting higher frequency signals in a first, higher bandgap material and transmitting lower frequency waves with photon energy below the material bandgap allows their subsequent conversion in lower bandgap materials allow better light capture, reduces color artifacts, and simplifies processing.
Three separate transducers are generally used in high end applications. Incoming light is separated to the three primary colors, either by filters, prisms, dichroic mirrors and the like, and each primary color impinges on a single transducer dedicated to that color. The use of three transducers, combined with the color separation system increases camera size, and is expensive using presently available methods.
There is a long felt and heretofore unsolved need for better technology, providing inexpensive, sensitive high quality electromagnetic (EM) energy image array sensors, and preferably sensor technology which may be made broad band, and/or polarization sensitive.